Method of treating petroleum oils



Patented Apr. 20, 1943 v 2,317,054 METHOD OF TREATING PETROLEUM OILS Lawrence M. Henderson, Winnetka,

and George W. Ayers, Jr., Chicago, 111., assignors to The Pure Oil Company, of Ohio Chicago, 111., a. corporation N Drawing. Application April 6, 1940,

Serial No. 328,242

14 Claims.

This invention pertains to the process of removing weakly acidic organic substances from hydrophobe organic liquid mixtures. The process is more particularly concerned with the removal of weakly acidic organic sulfur compounds such as mercaptans or thio-alcohols from petroleum oils and to the sweetening of sour petroleum distillates.

It is common practice in the petroleum industry to remove Weakly acidic sulfur compounds such as mercaptans from petroleum oils, particularly the lower boiling distillates such as gasoline, kerosine and furnace distillates, or to convert mercaptans into less objectionable compounds. The principal reasons for eliminating mercaptans from petroleum distillate is to effect an improvement in the odor and a reduction of the sulfur content of the distillate. The offensive odor imparted to petroleum distillates by relatively small quantities of mercaptans is a distinct detriment to the marketability of the gasoline. It has also more recently been established that the presence of organic sulfur compounds in motor fuels materially detracts from the antiknock quality of the fuels. This is particularly true when the motor fuels contain an antiknock agent such as tetraethyl lead, the amount ,of such agent required to produce a given antiknock rating in a motor fuel being substantially higher in those fuels of higher organic sulfur content.

By far the most widely used method heretofore for eliminating the offensive odor in sour or mercaptan bearing distillates has been to treat the distillates with a sodium plumbite or doctor solution. Although this method of treatment is satisfactory insofar as improvement of odor is concerned, it is open to several serious objections. In the first place, it is very difficult to control the amount of free sulfur used with the sodium doctor sweetening reaction and any excess of free sulfur causes the distillate to be corrosive and degrades the distillate in anti-knock proper ties. Furthermore, the sodium plumbite treatment does not remove the mercaptans but simply converts them to other organic sulfur compounds whichare innocuous insofar as odor is concerned, but which are very detrimental to the anti-knock properties of the gasoline. It is apparent that the degrading influence of the original sulfur on the anti-knock properties has not been eliminated when it is understood that the same amount of sulfur or perhaps more, due to the possibility of an excess of sulfur having been added to complete the sodium plumbite treating operation, is still in solution in the distillate.

Aqueous solutions of sodium hydroxide of various concentrations have also been used to plumbite solution to complete the remove weakly acidic organic sulfur compounds from petroleum distillates but are subject to the disadvantage that the weakly acidic sulfur compounds, particularly higher molecular weight alkyl mercaptans such as butyl and amyl mercaptans, are not removed or are only incompletely removed, the treated distillates continuing to possess an offensive odor and to be sour to the doctor test.

When aqueous alkali solution has been used to effect the removal of weakly acidic organic compounds from petroleum oils, the alkalinity of the caustic soda solution is reduced in proportion to the amount of acidic compounds extracted. The original alkalinity of the solution may frequently be substantially restored by steam stripping the used solution whereupon the reaction products of the alkali and weakly acidic sulfur compounds hydrolyze to release free alkali and the original acidic organic compound, the weakly acidic organic compound passing overhead as such with the steam. An example of such an operation is the steam stripping of aqueous sodium hydroxide solutions which have been used to remove alkyl mercaptans such as ethyl mercaptan, from gasoline. In the presence of water and at temperatures of the order of about F. to 300 F., the hydroxidemercaptan reaction product hydrolyzes to free sodium hydroxide and ethyl mercaptan, the ethyl mercaptan distilling from the aqueous sodium hydroxide solution. In this manner the restored or regenerated alkali solution may be used repeatedly, the loss of efficiency on each regeneration cycle being relatively small.

It has now been found that aqueous alkali solutions which have been used to treat certain petroleum oils, particularly certain relatively low boiling petroleum distillates, contain certain constituents which enhance the ability of the alkali solution to remove weakly acidic organic sulfur compounds from petroleum oils to such an extent that such oils can be rendered sweet to the doctor test by such treatment.

It is an object of this invention to remove weakly acidic organic compounds from hydrophobe organic liquids.

It is another object of this invention to provide a method for the removal of mercaptans from petroleum oils.

It is a still further object of this invention to provide a novel treating reagent for desulfurizing hydrocarbon oils and a method for preparing the same. v

Still another object of this invention is to provide a method of rendering sour hydrocarbon distillates sweet to the doctor test.

Other objects and advantages will be apparent from the following description.

In accordance with this invention it has been found that when aqueous alkali solutions are used for the treatment of certain petroleum 0115, especially certain relatively low boiling petroleum distillates, the used solution is more effective for the removal of weakly acidic organic compounds than is a fresh aqueous alkali solution of equivalent free alkali content. For a given free alkali content, the extraction eificiency of such solutions increases rapidly as the concentration of non-hydrolyzable extracted constituents increases. In order to maintain the extraction eillciency of the used solutions as high as pos-\ sible, it is preferable to regenerate such used solutions by heating or steam stripping in order to remove readily hydrolyzable components such as alkali mercaptides'and then adding, if necessary, an additional amount of free alkali to attain the desired alkalinity. Although an attempt has been made to analyze the used alkali and a number of compounds have been identified, it is not definitely known what compound or compounds are responsible for the greatly increased extraction efficiency of the used aqueous alkali solution. A list of the acidic organic compounds which have been identified in petroleum. and petroleum dist-illates which when treated with alkali give a reagent having the desired characteristics, is given in Table I:

Table l Thio-phenol o-Thlo-cresoi p-Thio-cresol Formic acid Acetic acid Iso-butyric acid Iso-valeric acid Phenol Naphthenic acid o-Crescl m-Cresol Not all petroleum oils contain all of the organic acidic materials shown in Table I, nor do all crude oils or petroleum distillates contain substantial quantities of any acidic bodies whatever their composition may be. Petroleum oils which impart the desired extraction efficiency to aqueous alkali solutions have been found to be those petroleum oils containing organic acidic constituents and especially those oils which possess an organic acidity of 0.05 or preferably 0.1 or higher, as determined by A. S. T. M. procedure Dl88-27T, which acidity is over and above that due to naphthenic acid. Alkyl mercaptans do not titrate as acidic constituents in the A. S. T. M. method of determining acidity. Examples of such oils are Texas crude oil known as Van Zandt and the cracked and straight run distillates obtained therefrom.

In a specific example which is offered by way of illustration only, aqueous sodium hydroxide solution, which had been used to treat a mixture of cracked and straight run gasoline of approximately 400 F. end point obtained from a mixture of Van Zandt and Schuler crude oils and having an A. S. T. M. neutralization number of approximately 0.95 of which approximately 0.4 was due to naphthenic acids, was regenerated by steam stripping at a temperature of approximate- 1y 250 F. and the solution concentrated by boiling oil excess water. A sample was reduced in volume from 20,000 cc. to a volume of 3,000 cc. The concentration of the solution was carried out in order to more clearly show the unusual results obtainable. The concentrated regenerated solution was tested and found to contain 14.6% by weight of free sodium hydroxide and approximately 55% by Weight of non-hydrolyzable reaction products of sodium hydroxide and organic acidic compounds. The extraction efli- 7 .volume water washes.

ciency of this solution for the removal of mercaptan sulfur from untreated gasoline as compared with that of fresh aqueous sodium hydroxide solution of equivalent sodium hydroxide content was tested. The data obtained are shown in Table II:

Table 1 Fresh sodium gg gg gg Treat 533 2? hydroxide Mam treating mun:

Percent cm! M's: ton 1n? n Original gasoline $014 0314 ii .0132 .0062 #2. .0094 .0021 #3. .0073 .0000 H. .(DM .oooss {5 .0004 Doctor test. to Sour Sweet Each treat consisted of the application of 10% by volume of treating reagent to a sample of gasoline and the gasoline and reagent contacted with agitation for a. period of fifteen minutes. Each treatment was followed by two 10% by New samples of treating reagents were used for each separate treat. The data in Table 11 clearly show the superior extracting efficiency of the used sodium hydroxide reagent. With this reagent it was possible upon the application of five successive portions to so completely remove mercaptan sulfur as to render the gasoline sweet to the doctor test. This was not possible when the same amount of fresh sodium hydroxide solution was used as the treating reagent, the concentration of mercaptan sulfur in the gasoline in the latter case being over twelve times that of the gasoline treated with the novel treating reagent. The odor of the sample of sweet gasoline was much better than that of the sour gasoline as might be expected by the doctor test. The gasoline used for illustration in Table II was hydrogen sulfide free and in general it is preferable to remove hydrogen sulfide in order to avoid the accumulation of sodium salts thereof, although the treating reagent is not limited in its application to such distillates.

While sodium hydroxide has been used in the specific example given, aqueous solutions of various alkalies may be used, other alkali metal hydroxides such as potassium hydroxide being particularly satisfactory. Concentration of free alkali in the aqueous alkali solution may vary within rather wide limits, although in general it is preferred to use solutions containing between approximately 10% and 40% by weight of caustic alkali. The amount of substantially non-hydrolyzable reaction product of caustic alkali and organic acidic materials should exceed 5% by weight and preferably not less than 15% of the caustic alkali solution. The upper limit of concentration is determined by the solubility of such reaction product in the particular caustic alkali solution that is used. In general, not over saturation of the caustic alkali solution is preferred. Since it has been determined that the extraction eiilciency decreases with increasing temperature, the extraction temperature is preferably maintained below approximately F. Extraction temperatures below approximately 35 F. can be employed but are not preferred as such temperatures may be unsatisfactory due to possible precipitation from the treating reagent of dissolved substances which aid in the extraction operation. The speed with which the aqueous alkali solution separates from the organic liquid being treated is ordinarily less at lower temperaiures and for this reason also, temperatures below approximately 35 F. may not be desirable.

The extraction ofthe weakly acidic organic compounds from organic liquids may be carried out in any one of a number of ways. Simple batch agitation may sufllce or a more thorough extraction may be had in a multi-stage countercurrent extraction system. The amount of used aqueous alkali reagent required for the extraction operation is normally above approximately 2% by volume of the oil or distillate treated and generally ranges from approximately 5% to 20% by volume although greater and lesser amounts may be used.

Aqueous alkali treating reagent prepared in accordance with this invention, that is, aqueous alkali solution which has been used to treat petroleum oil having an organic acidity of .05 or higher as determined by A. S. T. M. procedure D188-27T, which acidity is due to organic acidic constituents over and above that due to naphthenic acid, may simply berepeatedly used to extract weakly acidic material from organic liquids until the free alkali content of the treating reagent is below that at which satisfactory extraction efficiency is obtained, at which time additional free alkali may be added to restore the alkalinity to the desired level; or the free alkali content of such treating reagent may be maintained at the desired concentration by addition of fresh alkali such as sodium hydroxide after each treat, or the alkalinity may be restored by regenerating the used solution by boiling and/or steam stripping after each treatment or after any desired number of treatments and additional alkali added after regeneration to restore the original alkalinity of the solution. In a multiple step counter-current treatment of oil with reagent, it is preferable to regenerate the reagent and restore its alkalinity each time it passes through the entire series of treating steps.

The process herein disclosed is applicable not only to cracked and straight run gasoline, but to other essentially water insoluble, neutral or basic organic liquids as well as other petroleum captans from petroleum oils comprising contact- 5 ing said oils with aqueous alkali metal hydroxide reagent containing reaction products prepared by contacting light petroleum distillates obtained from crude oils containing organic acidic constituents including naphthenic acids, phenols and thiophenols with aqueous sodium hydroxide solution under conditions to react sodium hydroxide with organic acidic constituents present in said distillates, followed by steam stripping the aqueous sodium hydroxide solution of hydrolyzable constituents and concentrating the stripped solution to a content of not less than approximately of reaction products.

2. Process in accordance with claim 1 where the reaction products include the reaction products of sodium hydroxide and formic, acetic, isobutyric, iso-valeric and naphthenic acids, phenol and thio-phenol, o-cresol and o-thiocresol and rn-cresol and p-thiocresol.

3. A step in the process of removing mercaptans and other weakly acidic organic compounds contained in water insoluble hydrocarbons comprising contacting said hydrocarbons with used and regenerated alkaline reagent containing not less than approximately 15% by weight of reaction products of alkali metal hydroxide and organic constituents which are acidic as determined by A. S. T. M. procedure Dl88-27T said reaction products resulting from the reaction of said alkali metal hydroxide solution with organic acidic constituents in hydrocarbon distillates.

4. A step in accordance with claim 3 where the reacting organic acidic constituents include thiophenols.

5. A step. in accordance with claim 3 where the alkaline reagent is an aqueous reagent containing approximately 10% to 40% by weight of free alkali metal hydroxide.

6. A step in accordance with claim 3 where the reaction products include the reaction products of alkali metal hydroxide and formic, acetic, isobutyric, isovaleric and naphthenic acids, phenol. thio-phenol, o-cresol, o-thiocresol, m-cresol and p-thiocresol.

7. A step in the process of removing mercantans from petroleum oils comprising contacting said petroleum oils wi t reagent produced by contacting petroleum oil containing organic constituents which are acidic as determined by A. S. T. M. procedure D188-28T with aqueous alkali metal hydroxide solution under conditions to re-.

act alkali metal hydroxide with at least a portion of said organic acidic constituents and concentrating the resulting aqueous solution to a content of not less than approximately 15% of reaction products to form the desired reagent.

8. A step in accordanc with claim 7 where the aqueous solution is also stn'pped of hydrolyzable constituents.

9. A step in accordance with claim 7 where the reacting organic acidic constituents include thiophenols.

10. A step in accordance with claim '7 where the acidic constituents reacted with alkali metal hydroxide include formic, acetic, iso-butyrlc, isovaleric, and naphthenic acids, phenol, thiophenol, o-cresol, o-thiocresol, m-cresol and pthiocresol.

11. A step in accordance with claim 7 where the reagent contains approximately 10% to 40% by weight of free alkali metal hydroxide.

12. A step in accordance with claim 7 where at least a p o of the reacting organic acidic constituents are constituents other than naphthenic and fatty acids and which are acidic in accordance with A. S. T. M. method D188-27T.

13. The step in accordance with claim 3 in which the reagent contains 10 to 40% by weight of free alkali metal hydroxide and the petroleum oil from which the acidic constituents are obtained has an acidity as determined by A. S. T. M. procedure Dl88-28T of at least .05 over and above acidity due to naphthenic acids.

14. The step in accordance with claim 1 in which aqueous alkali metal hydroxide reagent contains from 10 to 40% by weight of free alkali metal hydroxide.

LAWRENCE M. HENDERSON. GEORGE W. AYERS, J R. 

